1. Field of the Invention
The present invention relates to a stepping motor drive control system suitable for a facsimile system, or more particularly, to a stepping motor drive control system which optimizes precision in rotation of a motor.
2. Related Background Art
Stepping motors are used for sheet transportation in facsimile system. A stepping motor is driven by one step angle in response to a step drive command. The motor drive can be controlled so easily that sheet feed in a facsimile system can be done continuously or intermittently, or stopped temporarily, depending on the step drive command. The time from when a step drive command is provided to the stepping motor of a facsimile system until when the next step drive command is provided is rarely uniform and often variable. With a stepping motor, the intervals of step drive commands can vary largely. Therefore, the stepping motor has come to be used for a facsimile system.
FIG. 1 shows a general response characteristic of a stepping motor in a case where a stepping motor is driven with a step drive command. A rotor of the stepping motor attains to a stable state while converging vibrations. The stepping motor shows such a response characteristic. In a stepping motor employed for a prior facsimile system, a minimum response time shown at A in FIG. 1 is determined, and the next drive command is applied after time A when the rotor has attained a one step angle.
Therefore, the aforesaid prior stepping motor for facsimile systems would be effective for continuous drive control making the intervals of step drive commands uniform. However, when the intervals of step drive commands vary largely, the problems noted below attributable to the response characteristic of the stepping motor are inevitable.
When the intervals of step drive commands vary largely, a next step drive command may be applied during time B or time C in FIG. 1. During times B and C, the angular position of a rotor varies greatly. The directivity of the rotor varies largely, too. For sheet transportation in a facsimile system, the inertial force and backlash of a driving system are added. Comparing the operation when the next step drive command is applied during time B in FIG. 1 and the one when the next step drive command is applied during time C in FIG. 1, one sees that the operating states of a stepping motor are completely different. When the next step drive command is applied during time B in FIG. 1, the stepping motor is oriented in the rotating direction. Therefore, the operation of the stepping motor is stable. When the next step drive command is applied during time C in FIG. 1, the stepping motor is oriented inversely from the rotating direction. Therefore, the operations performed by the stepping motor are unstable. This causes noise and vibrations during sheet transportation in a facsimile system.
The aforesaid problems are negligible for an expensive system equipped with a stepping motor having a sufficient size and a highly precise structure, but they are very serious for a compact and low-price system.
Facsimile systems have become popular into our society. There is a growing demand for a compact and low-price system that performs with high precision. A stepping motor employed for such a system has been designed to be compact and low-price. Therefore, the aforesaid problems associated with the stepping motor employed for a compact and low-price facsimile system are gaining people's attention.